The invention concerns an apparatus for suspending at least one current-carrying contact wire for current collectors of overhead line buses or trams, with a mechanical connecting device, in particular a clamping device, which can be fixed to a support cable or the like elongate member, and a connecting element which is insulated relative to the support cable and to which is connected a gripping member for the contact wire.
A trolley or contact wire which is suspended in a point-like fashion at two support cables which cross at a spacing from each other the route of the overhead line bus--also referred to as a trolley bus--, the tram or like vehicle, forms generally a catenary curve. It extends horizontally in the middle between the two support points and rises progressively more steeply to the suspension points. The position of the contact wire is dependent on its specific tension and the distance between the two suspension arrangements.
When the contact wire is in rubbing contact with a trolley bus current collector or pantograph, the contact pressure of that sliding contact member urges the contact wire upwardly out of its rest position into what is referred to as its working position. The difference in height between the rest position and the working position is at its greatest in the middle of the span length of the cable and at the smallest at the support point, and it is dependent on the contact pressure of the sliding contact member, the span length, the specific tension of the contact wire, its cross-section, and the speed of the vehicle or sliding contact member.
The curve of the working position substantially corresponds to the rest position, that is to say, it is horizontal in the middle of the span length and at the steepest at the support point.
When now the sliding contact member slides along the working line, initially it is still in an almost horizontal configuration. Then, as the curve of the contact wire becomes progressively steeper, the sliding contact member must be accelerated upwardly more and more. However, there is a limit on that capacity for acceleration of the current collector, due to the mass inertia and the contact pressure involved. The sliding contact member can no longer follow the curve of the contact wire as it becomes progressively steeper, at higher speeds, comes away from the contact wire before reaching the support point, jumps over the support point and, after the support point, hits against the contact wire of the next span length. That springboard effect which occurs in relation to rigidly suspended contact wires can be easily noted due to the presence of sparks just before and after the suspension point.
That jump-off effect is further promoted by a contact wire wave which the current collector pushes along in front of it. It is reflected at the fixed suspension point and further contributes to throwing the current collector off in a downward direction. Besides radio interference, this phenomenon of the current collector jumping off the wire gives rise to weld beads in particular at the point of impingement and also results in increased mechanical wear of the contact wire. The weld beads in turn have a damaging effect on the sliding contact member.
The foregoing problems have been substantially alleviated by virtue of an elastic suspension configuration. Such apparatuses, of the general kind set forth above, with a ceramic insulating body between clamps which embrace the support cable, and a parallelogram-like suspension arrangement, are described in Swiss patent specification No 207 177 as an addition to Swiss patent specification No 195 513 to the present applicants. This known suspension arrangement comprises a pair of elongate suspension members and two yoke-like transverse elements which are connected by same and of which one affords clamps for the contact wire. The yoke which is near the cable is rigidly connected to the insulating body. The insulating body which is mounted in a bell-like metal hood with lateral plates and from which a screw pin projects downwardly is also to be found in Swiss patent specification No 186 137. In addition Swiss patent specification No 229 346 discloses a swing curve holder which is provided with the insulating body and in which a cantilever arm which presses towards the end against the support cable adjoins the metal hood of the insulating body.
If, in accordance with above-mentioned Swiss patent specification No 195 513, the contact line is laid along a straight line in a zig-zag configuration (maximum contact wire angle in a straight line of 21/2.degree.), then two force components occur at the suspension point. One of the force components is the weight of the contact wire, which is dependent on the span length, while the other is the curve tension which is dependent on the contact wire angle and the tension in the contact wire. If now the contact wire or contact line is suspended at the support point by means of a swing member, then, in accordance with those two components, that member will adopt a certain inclined position.
If the contact pressure of the sliding contact member changes the vertical component even only by a small amount, then the inclination of the swing member--and therewith also the height of the contact wire at the suspension point--is also immediately altered.
If the sliding contact member moves towards the support point, the contact pressure of the current collector increasingly takes over a part of the weight of the contact wire as it approaches the support point, that is to say the vertical weight component on the swing member is reduced, the swing member takes up a flatter position, and the contact wire is raised from the lower rest position into the upper working position at the support-point. The sliding contact member now comes entirely into the vicinity of the support point where the contact wire rises at its steepest. In order to remain on the contact wire, the current collector would have to accelerate upwardly very considerably, which is not possible when operating at higher speeds, by virtue of its mass inertia. The above-mentioned springboard effect would now occur, in the case of a rigid contact wire.
If now however the sliding contact member were to jump off the contact wire here, the contact pressure would naturally have to fall to zero beforehand. In such a situation, the vertical component would immediately become greater and greater at the swing member, that is to say the swing member becomes steeper and the suspension point moves downwardly. If therefore the sliding contact member can no longer cope with the rise in the contact wire before the support point, the suspension point with the contact wire which was initially urged upwardly moves downwardly towards the sliding contact member and contact is ensured.
When the sliding contact member has passed the support point, it jumps on to the contact wire at the next span length with a certain amount of weight, depending on its mass and speed. That horizontal force is divided into two components. One is directed tangentially relative to the contact wire and is therefore harmless; the other is upwardly perpendicularly to the contact wire and, if the contact wire is suspended rigidly, after the suspension point, it causes severe wear thereof.
However, in the case of the above-mentioned elastically suspended contact wire, that upwardly directed force component results in a reduction in the vertical component of the swing member and consequently the swing member takes up a flatter position, the suspension point rises and the contact wire elastically absorbs the impact of the sliding contact. However that is only possible in the case of a contact wire suspension arrangement using an inclined swing member; if the swing members were to be disposed vertically, the contact pressure of the current collector would first have to overcome the entire weight of the contact wire in a span width before the suspension point rises or becomes elastic. The contact wire is caused to oscillate by virtue of the contact pressure of the sliding contact member and due to the lateral sway of the trolley bus.
The superiority of the elastic contact wire suspension arrangement relative to the rigid arrangement lies in the upward and downward oscillation movements of the swinging support points in dependence on the contact pressure. Therefore, by means of a wire parallelogram, it is necessary to ensure that the contact wire is perpendicular in any swing member position.
The above-mentioned zig-zag configuration of the contact wire does not have any adverse influence on current pick-up as the low forces which occur, due to the lateral acceleration of the current collector at the support point, are readily compensated by the swing member. In addition, that zig-zag configuration in conjunction with the inclined swing members provides for partial compensation of the variation in tension of the contact wire, which is caused by temperature. That effect occurs by virtue of the fact that, at different temperatures, both the inclined positioning of the swing members and also the contact wire angle at the support point alter, and therewith the distance from one suspension point to another.
The above-discussed so-called inclined swing members afford the following advantages:
uniform contact pressure of the current collector as a result of resiliency or yielding nature of the contact wire at the suspension points;
a high level of operational reliability and a low risk of derailment;
freedom from radio interference;
a long service life for the carbon sliding members of the current collector without the contact wires having to be lubricated;
almost no wear of the contact wire; long service life and a saving on copper;
partial compensation for thermal expansion of the contact wire, that is to say the difference in tension;
possibility of using maximum span lengths of up to 35 meters in straight lines and thus a lower level of need for support masts;
lower maintenance costs and therefore greater operating economy; and
permitting very high speeds of travel, particularly in bends and curves, and an increase in economy of operation due to higher journey speeds.
Against the advantages of the swinging suspension arrangement, there is the disadvantage that the known swing member suspension arrangements are susceptible to wear in the region of their ceramic insulating bodies; the latter are highly sensitive to forces acting thereon from the outside.